1. Field of the Invention
This invention relates to medical access devices and, in particular, to expandable medical access devices for providing minimally invasive surgical access for various surgical procedures.
2. Description of the Related Art
A wide variety of diagnostic or therapeutic procedures involve the introduction of a device through a natural or artificially created access pathway. As such, minimally invasive access systems have been developed to generate such pathways. A general objective of these access systems is to minimize the cross-sectional area of the puncture, while maximizing the available space for the diagnostic or therapeutic instrument. Procedures that utilize access systems include, among others, a wide variety of laprascopic diagnostic and therapeutic interventional procedures.
In many of these procedures, it is advantageous to provide a self-retaining access system that provides tissue retraction throughout a surgical procedure without the continued attention of a human assistant. Self-retaining retraction provides the operator with the ability to choose the tissue and separation plane to provide adequate exposure for a given surgical procedure. Examples of tissues retractors commonly known in the surgical art include the Richardson retractor, the Alm retractor, the Balfour retractor, the Rigby retractor and the like.
In contrast to minimally invasive access systems, surgical approaches, by their open nature, generally require the elements of incision, dissection, hemostasis, and mechanical closure. The incision is typically accomplished using a scalpel, a saw, or an electrosurgical cutting device. Dissection is typically accomplished using a scalpel, electrosurgical cutting device, or a blunt object such as a pair of forceps or an obturator. Hemostasis control is generally performed using electrocautery, wound packing, and suction drainage to a collection system. Mechanical closure is generally accomplished using sutures, staples or clips.
Surgical approaches afford direct surgical vision, direct tactile feedback along with the intrinsic ability to enlarge the field of view simply by enlarging the incision and resetting the self retaining retractor. While large incisions may heal as quickly as small ones, they are a source of extended patient discomfort and poor cosmetics along with expensive recovery periods, both in and out of the hospital.
Many surgical procedures have been converted to minimally invasive, laparoscopic procedures that avoid large incisions, reduce hospital stays and costs while producing similar short- and long-term results. Such procedures typically involve minimally invasive access systems as described above. However, minimally invasive access systems for surgical procedures that do not invade body cavities, such as the abdomen or thorax may not be suited for traditional laparoscopic visualization. Such is the case in orthopedic procedures (e.g., joint or spine access). In these cases, a surgeon often is forced to rely on the blunt placement of consecutively larger cannula, with or without the benefit of a dilator to reach the desired surgical site. Surgical instruments are then inserted through the cannula to reach the target site. Surgical exposure is limited by the accurate placement of the cannula, location of pathology and diameter of the cannula. Once the skin incision of adequate size is made, the axial shear force of sequentially placed dilators, with increasing diameters, creates an operative tunnel to reach the desired surgical site.
The rigid walls of the cannula exert a tamponade pressure to provide hemostasis during the session. Distal visualization is often provided by a rigid scope while operative maneuvers are accomplished with laparoscopic or extended length instruments placed through the cannula. Radial pressure holds the cannula over the operative site freeing the operative team from retraction duties as well as removing potential obstructive nuisances from the immediate surgical field. Enlarging the surgical field requires placement of a larger cannula with an axially directed shear force. Such placement of a new cannula carries with it the possibility of loosing anatomic landmarks during the device transition. Since a majority of the tissue plane separation is achieved with blunt expansive force, rather than by tissue shearing, and is maintained with radial force, recovery is often less traumatic than that encountered with open surgery. Should the operative procedure require expansion with incision and traditional retraction applied, the recovery course may be longer and costs higher than if the minimally invasive approach was used.
Traditional laparoscopy also uses trocars, with diameters ranging from 5 to 20 mm, to gain access to the abdomen or chest. Most procedures are successfully completed through three or four trocar sites. There are cases, such as removing an organ or tissue for transplant, when time and labor burden could be reduced by the ability to enlarge a trocar site. Surgical incision sites must enlarged carefully, however, because most operators are reluctant to expand surgical exposure at the risk of losing the anatomic landmark.
A need therefore remains for improved access technology needed to create a tunnel to a target surgical site in such a way that trauma to the tissue is minimized. Preferably, such technology provides for controllable tissue dilation once the initial tunnel is created.